Method and apparatus for containing of molten metal in a glass sheet float apparatus

ABSTRACT

GASEOUS ACCUMULATIONS ARE AVOIDED ON THE REFRACTORY BLOCKS OF THE TANK STRUCTURE SUPPORTING A BATH OF MOLTEN METAL ALONG WHICH GLASS IS ADVANCED IN THE FLOAT PROCESS FOR THE MANUFACTURE OF FLAT GLASS, BY APPLYING A NEGATIVE PRESSURE TO A RESTRICTED INTERSPACE SURROUNDING THE REFRACTORY BLOCKS AND SEALING OFF THE HEADSPACE FROM THE INTERSPACE TO INTERCEPT DIRECT GAS FLOW FROM THE HEADSPACE INTO THE INTERSPACE.

Jane 8, 1971 J. LAWRENSQN ET AL METHOD AND APPARATUS FOR CONTAINING OFMOLTEN METAL IN A GLASS SHEET FLOAT APPARATUS 2 Sheets-Sheet 1 Filed May26, 1969" Inventors JACK LAWRENSON & ALBERT SIDNEY ROBINSON June 8, 1971LAWRENSON ETAL 3,583,859

METHOD AND APPARATUS FOR CONTAINING 0F MOLTEN METAL IN A GLASS SHEETFLOAT APPARATUS Filed May 26, 1969 2 Sheets-Sheet 2 Inventor- JACKLAWRENSON & ALBERT SIDNEY ROBINSON United States Patent Of 1m. Cl.C03b18/02 US. Cl. 65-32 4 Claims ABSTRACT OF THE DISCLOSURE oRoss REFERENCESTO RELATED APPLICATIONS v This application is a continuation-impart toour copending application Ser. No. 508,357 filed Nov. 17, 1965, nowabandoned.

BACKGROUND OF THE INVENTION This invention relates to the containing ofmolten metal and more especially to containing structures for moltenmetal, for example in glass manufacturing processes and apparatustherefor during which glass is brought into contact with a bath ofmolten metal.

Industrial processes are well known in which molten glass is fed on to abath of molten metal and a ribbon of glass developed on the bath fromthe molten glass supplied to the bath. It is also known to improve thesurfaces of a rolled ribbon of glass by delivering the cast also beenemployed. Tin is a very expensive metal and:

many tons are employed in constituting the bath. Also tin is readilyoxidised at the high temperatures in which it is used, e.g. 1000" C. andhas to beprotected from effects of furnace gases of glass meltingfurnaces. To protect the tin a plenum of a protecting gas is maintainedwithin a roof structure over the bath to prevent ingress of atmosphericair or other gases which can be harmful to the tin.

The refractory structure used to contain the molten bath, in theprocesses referred to, may be constituted by assembling blocks ofrefractory material arrayed in close juxtaposition, and to allow forexpansion of the blocks they are so assembled that interstices existbetween them. The molten bath contained by the structure so erectedproduces an interface where the bath lies against the refractory wallsi.e. the side and end walls and the floor of the structure.

In operation there may be a tendency for gases to col- 3,583,859Patented June 8, 1971 lect in the interstices between abutting blocks,resulting in an accumulation of gases in the interstices, and a pressurebuild up may occur in the interstices so that these gases then rise andmove in to areas of progressively higher temperatures, so that theirvolumes increase as they traverse the interstices and ultimately find away into the tin/refractory interface and spread into the tin in theform of bubbles.

A main object of the present invention is to rid the refractory walls ofthe gaseous formations wherever they may occur, as an insurance againstentry of bubbles into the molten metal bath.

SUM MARY The present invention involves a method of using a structurecontaining a molten metal bath having a headspace 1n which a plenum ofprotecting gas is maintained and haying a support structure of abuttingrefractory blocks in which the molten metal bath is contained and withinterstices between juxtaposed surfaces of the blocks in communicationwith a common restrictive interspace defined by said refractory blocksand an enveloping shell, which method includes sealing off the headspacefrom the interspace and applying a negative pressure to the interspaceand to the interstices communicating therewith whereby to insure againstentry of bubbles from said lnterstices into the molten metal bath.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates diagrammaticallyapparatus for preventing gaseous formations in interstices at the jointsbetween abutting refractory blocks assembled to constitutg a containingstructure for a bath of molten metal; an

- FIG. is a vertical transverse cross-section through the containingstructure illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 of thedrawings, adjacent refractory blocks forming part of the bottom wall orfloor of a tank structure are indicated at 1, 2 and 3, which tankstructure contains a bath of molten metal indicated at 4. The moltenmetal bath has the characteristics fully de-' scribed in US. Pat. No.2,911,759. The lower plane surr-ibbonr on to a bath moltenmetal so hsurface i face of the bath is indicated at 5 and the tank structurecontiguity with the floor of the tank structure as indicated at 6. Arestricted interspace indicated at 7 is provided between the relativelysmooth inner surface of the metal and the rough outer surfaces of thejuxtaposed refractory blocks.

Between the floor refractories exemplified at 1, 2 and 3 and the bath 4,is an interface of large surface area in which the plane molten face 5at the bottom of the bath lies in contact with the inner relativelyrough faces of the blocks 1, 2 and 3. The usual interstices 8, 8 ofrelatively small volume between refractory blocks such as 1, 2 and 3 aregreatly exaggerated for the sake of clarity.

All the walls of the tank structure, that is the side walls, the two endwalls and the floor, are formed of adjoining refractory blocks and thewhole tank structure is encased in the shell of welded steel sheet.

The shell 6 is apertured as indicated at 9 to form the entry to a duct10 in a bushing 11 secured e.g. by welding to the shell 6. At the outerend of the bushing is mounted v through which a cooling medium,preferably water, is continually circulated in contraflow via an inlet15 and outlet 16. Any molten metal of the bath which finds its way intothe interspace and through the outlet 9 is solidified and caught in theheat exchanger.

The heat exchanger flow pipe 13 is connected to a branch 17 leading to amanifold 18 to which manifold a plurality of ducts 9 in the shell 6leading out of the interspace 7 is connected. Each branch may have avacuum gauge 19.

The manifold 18 is connected by piping 20 to a vacuum pump indicated at21. The line 20 may have a bleed valve 22 as indicated and a vacuumgauge 23. Several manifolds each with branches leading to the interspace7 may be connected with pumps to ensure uniformity of the negativepressure in the interspace.

Exactly similar arrangements may be erected outside the side walls andend walls (not shown) of the tank structure in order that the interfacesurrounding the bath will in turn be surrounded by interspace 7.

In operation the pump applies a negative pressure to the interspace 7and thence to the interstices 8, which may in some instances bepartially filled by molten metal extending down into the interstices asindicated at 25. In other instances the negative pressure may be appliedthrough the interstices 8 to the interface where the plane face of thebath and the relatively rough faces of the blocks such as 1, 2 and 3meet. The negative pressure at the interface is always sufiicient toengender migration of gas from the interface into interspace 7 as shownby arrows 24 and thence into extracting system 10, 13, 17, 18 and 20 ofthe pump system.

The apparatus described prevents the formation of any bubbles so thataeration of the molten metal is prevented and ensuing arrival of bubblesat the interface between the ribbon of glass and the bath prevented.

Where a protective atmosphere is maintained at a plenum in the headspacedefined over the containing structure some gas from the headspace mightreach the interspace between the metal casing and the refractory blocksby downward gas flow from the headspace to the interspace for examplethrough the porous refractory blocks.

Such direct gas flow from the headspace into the interspace isintercepted as illustrated in FIG. 2 by facing the top edges 25 of thetank structure with metal plates 26, or by employing a suitable sealingmedium in place of the metal plates 26 at the top edges of the tankstructure, to seal any passages through the top surfaces of the tankside and end walls.

In the foregoing description reference is made to an elongated tankstructure containing a bath of molten metal and the protection of themolten metal against aeration and contamination during the production ofglass in ribbon form on a bath of molten metal, either by manufacturingthe ribbon on the bath or by improving the surfaces of a rolled ribbonfed on to the bath.

The use of the invention, however, is not limited to this field ofoperation, but the invention can be used in any glass manufacturingprocess during which the glass is brought into contact with a bath ofmolten metl.

We claim:

1. In the operation of a float glass manufacturing apparatus having acontainer structure for a bath of molten metal which has walls ofabutting refractory blocks with interstices between adjacent facesthereof and which is enveloped in a shell, and said apparatus havingalso a roof for the container structure including refractory blocksdefining an enclosed headspace above the molten metal bath, the stepswhich include advancing a ribbon of glass along and while supported onsaid 'molten metal bath, maintaining a plenum of protective gas in theheadspace above said molten metal bath, applying a negative pressure tothe interspace and to the interstices communicating therewith whereby toinsure against entry of bubbles from said interstices into the moltenmetal bath, and impermeably sealing off the wall structure throughoutsubstantially the width thereof at a level adjacent the level of themolten bath substantially to deny access to the inerstices in the wallsof the container structure, of plenum gases otherwise drawn from theheadspace through the refractory blocks of the roof.

2. A method according to claim 1, wherein the negative pressure appliedis from inch to 7 inches water gauge below atmospheric pressure.

3. A float glass manufacturing apparatus comprising walls of abuttingrefractory blocks having interstices between juxtaposed faces thereofand forming a container for a bath of molten metal having a surface onwhich a ribbon of glass is supported during manufacture, a roof over thecontainer having a lining of refractory blocks defining an enclosedheadspace above the metal bath for containing a plenum of protecting gasfor the molten metal, a shell enveloping the refractory block containerand defining therewith a restricted interspace in communication with theinterstices between the blocks, means ineluding an external pumpingsystem communicating with the interspace through said shell forexhausting gases from the interspace and from the intersticescommunicating therewith, and gas impermeable means extending across thewidth of said walls substantially at the level of the molten metal inthe bath and forming a barrier to the withdrawal of plenum gas throughsaid refractory roof lining into the zone affected by the pumpingsystem.

4. Apparatus according to claim 3, wherein the pumping system includes aheat exchanger in which molten metal withdrawn from the interspace issolidified.

References Cited UNITED STATES PATENTS

